PROJECT SUMMARY/ ABSTRACT Young children who have experienced neglect or abuse are at increased risk for poor behavioral and biological outcomes. However, this risk can be buffered if their parents behave in sensitive ways. Attachment and Biobehavioral Catch-up (ABC), a home visiting intervention, targets parental sensitivity among parents of high-risk infants. Through efficacy trials, the ABC intervention has been shown to engage the intervention mechanism, parental sensitivity, and enhance parental neural activity. In addition, children whose parents receive the ABC intervention show better outcomes in attachment, cortisol production, and behavioral regulation than children whose parents receive a control intervention. Pilot work suggests that some parents respond to the intervention within several sessions, suggesting that an abbreviated intervention could be optimal for them. The next critical step is demonstrating that the ABC intervention engages the intervention mechanism when implemented by community clinicians in a community context, and examining whether some parents can benefit from an abbreviated version of the intervention. This effectiveness trial leverages an existing partnership between a community-based organization and child welfare system to examine whether the ABC intervention engages the treatment mechanism, parental sensitivity, when implemented by community clinicians, whether changes in parental sensitivity mediate intervention effects on child outcomes, and whether parental cumulative risk moderates the effectiveness of varied dosages of the intervention. A total of 360 parents and their young children involved in the New York City child welfare system will be included as participants. Parents will be randomized to a screen-and-refer intervention with an established evidence base (Safe Environment for Every Kid; SEEK), to SEEK plus a 3-session version of ABC (ABC 3), or to SEEK plus the standard 10-session ABC intervention (ABC 10). Intervention effectiveness will be examined as changes in parental sensitivity (the intervention mechanism) at both behavioral and neural levels, as well as changes in child outcomes. Changes in parental sensitivity are expected to mediate intervention effects on child outcomes. Individual differences in response to treatment dosage will be explored.